In recent years, there have been introduced illumination light sources which use LEDs as light sources, in view of energy saving.
FIG. 23 is a partial cross-sectional view of an illumination light source according to a related art. Illumination light source 1100 includes light emitting module 1110 having LEDs, circuit unit 1120 to make light emitting module 1110 light up, and case 1130 with a substantially-cylindrical shape to accommodate circuit unit 1120. On the outer wall of case 1130, a plurality of radiation fins 1140 with a flat-plate shape is radially disposed.
Generally, illumination light source 1100 is mounted on a ceiling and the like, in the vertically downward direction. In this mode of usage, when illumination light source 1100 lights up, heat is generated by such as light emitting module 1110 and circuit unit 1120 to warm surrounding air of illumination light source 1100. This generates air streams around illumination light source 1100, which flow in the vertically upward direction. The air streams flowing vertically upward can smoothly pass through gaps between radiation fins 1140, which allows every radiation fin 1140 to perform heat exchange with outside air.